Prevalence of plant-parasitic nematodes in nethouse tomato production in Limpopo Province, South Africa, and relationships with physico-chemical soil properties

Continued monocropping practiced by commercial farmers in protected nethouses provides the ideal environment for crop growth but makes it more vulnerable to infection by plant-parasitic nematodes. With the objective to assess the development of plant-parasitic nematodes in nethouses, a pre-plant assessment of the nematode community was undertaken indicating the presence of 56 nematode genera in the 26 nethouses with 1/3rd being plant feeders. This was followed by a study of the population density development of the prevalent plant-parasitic nematodes on tomato plants in six nethouses during three consecutive years. The genus Meloidogyne (root-knot nematodes) was the most prevalent genus consisting of a mixture of three or four species: M. arenaria, M. enterolobii, M. incognita and M. javanica . The tomato rootstocks ‘RS3’ and ‘RS13’ appeared to be least susceptible to Meloidogyne infection. The highest population densities of Meloidogyne were observed in sandy soils. Higher values of Ca, K and pH were correlated with lower relative population densities (RPD%) of Meloidogyne and Pratylenchus , while higher values of %Mg and Mg:K were correlated with higher RPD% of Meloidogyne and Pratylenchus . The usefulness of the I Ca / I Mg ratio to monitor the application of nutrients affecting the susceptibility of tomato plants to Meloidogyne infection should be further investigated.